The invention relates generally to methods, semiconductor devices, electrical and electronic circuits, and products useful in acoustic distance measurement systems, and particularly acoustic echo distance measurement systems.
Acoustic distance sensing and distance measurement systems have been in use for years in a variety of applications. These systems generally operate by transmitting a short pulse of acoustic energy, creating a sound wave in the ambient air, and measuring the time it takes to receive an echo of the pulse, which indicates the distance to the object that reflected the acoustic pulse. The closer the echo-producing object, the shorter the time of arrival of the echo at the sensor after the transmission.
To commence transmission of an acoustic pulse, an electric signal is applied to an acoustic transducer to cause the operative part of the transducer to vibrate in correspondence with the electric signal. However, when the signal is ceased or removed from the transducer, the transducer continues to vibrate during a period referred to as “ringdown” or “reverberation.” The duration of the reverberation depends on the quality factor of the transducer. During ringdown the frequency of the transducer vibration is at its natural or resonant frequency and the duration of this period depends on the quality factor of the transducer. If the frequency used to drive the transducer is not the same as the transducer's natural frequency, the vibration frequency of the transducer transitions from the driving frequency to the present natural frequency of the transducer during the reverberation period, and the magnitude of the transducer vibration decays during the reverberation period. In systems where the transducer is used for both transmitting and receiving, the ringdown or reverberation period typically prevents detection of echo signals received during the reverberation period (i.e. echoes produced by objects very close to the transducer). Practically, it can easily result in a flawed distance measurement (in case of multiple reflections which can overlap), or even a situation where an echo is missed completely because it is obscured by the reverberation or because the system just doesn't attempt echo detection during the reverberation period. Accordingly, there is a need to be able to detect echo signals received during the reverberation period of a transducer and to determine when multiple echoes are overlapping.
The drawings are meant to illustrate examples of some embodiments that can be implemented in accordance with the teachings herein. Variations within the teachings and the claims within the full scope of the embodiments will occur to those skilled in the art.